Merosin Deficient Congenital Muscular Dystrophy type 1A (MDC1A) is a devastating neuromuscular disease caused by mutations in the LAMA2 gene and loss of laminin-?2 protein. MDC1A patients exhibit severe muscle weakness from birth, are confined to a wheelchair, require ventilator assistance to breathe and have reduced life expectancy. There is currently no effective treatment or cure for MDC1A and all affected children will die from this genetic disease unless treatments are soon discovered. Laminin-?2 is required for the formation of heterotrimeric laminin-211 (?2, ?1, ?1) and laminin-221 (?2, ?1, ?1) which are major constituents of skeletal and cardiac muscle basal lamina. Laminin-111 (?2, ?1, ?1) is the predominant laminin isoform in embryonic skeletal muscle and supports normal skeletal muscle development in laminin-?2 deficient muscle but is absent from adult skeletal muscle. We have recently shown that mouse laminin-111 protein can be systemically delivered to the muscle of laminin-?2deficient mice to prevent muscle pathology, maintain muscle strength and dramatically increase life expectancy. These findings demonstrate that laminin- 111 is a highly potent therapeutic in the dyW-/- mouse model of MDC1A. At the time of diagnosis, children with MDC1A have developed significant muscle disease and it is unclear if laminin-111 protein therapy is effective at preventing disease progression after it has already started. This proposal will investigate if laminin-111 protein therapy can prevent disease progression after onset, determine if recombinant human laminin-111 can prevent muscle disease and investigate the mechanism of protection conferred by laminin-111 protein treatment. We will test the hypothesis that laminin-111 protein can functionally substitute for laminin- 211 and serve as an effective therapeutic for MDC1A. We will test this hypothesis in three Specific Aims. First we will determine if laminin-111 prevents further muscle damage after disease onset, preserves muscle function and improves survival in the dyW-/- mouse model of MDC1A. Second we will determine if transgenic expression of human laminin-111, recombinant human laminin-111 or recombinant human laminin-211 improves preclinical outcomes in the dyW-/- mouse model of MDC1A. Finally we will determine scalability of laminin-111 protein therapy and define the pharmacokinetic and pharmacodynamic profiles in mouse and dog models. Results from this study will pave the way towards developing laminin-111 protein therapy as a novel therapeutic for MDC1A.